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E39 (1997 - 2003) The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

Can someone help me open the keyless entry for my 528i?
I think the battery is dying. I can't pop the trunk. I have opened many chrysler and jeep fobs before, but not one like this. It is a laser-cut key, with 3 buttons on one side, and the other side says " fcc id fzv. I can't make out the rest of it.

Insert key, turn, open trunk. Manual entry is a 90 degree turn to the left; 45 degrees will unlock and then you'll be able to push the button above the license plate.
Someone will be by shortly to post pictures of the various keys. 2001+ keys have the battery soldered to the board

If you have the old style key (rubber with the 3 buttons sort of in a triangle...2 on the bottom + 1 large LOCK button at the top...when you flip the key over, you should see a flap. Take a small screw driver or your fingernail to lift . This will expose 2 screws...undo those 2 screws and the entire back cover comes off.

You will need a 2016 battery which you can get from Walmart's jewelry counter, Radio Shack, or the watch kiosk at the mall.

Does your key look like this?

If yes, turn it over and lift the little flap which will expose 2 screws...

If that's the case...I'd still look at the keys battery. You just listed TWO of the things that indicate the battery is not performing up to snuff:

Doors don't lock

red LED does not flash

...a 2016battery can be picked up at Walmart, Radio Shack, local drug store, or the watch kiosk at the mall for a couple of dollars...just remember to buy the battery first then switch it out within 60 seconds so that you won't have to reinitialize the key

Or perhaps your button is worn and needs to be adjusted etc...IF you open your key to check the buttons from the inside...MAKE SURE YOU DON'T LOSE THE TRANSPONDER/CHIP...it sits loose inside your "old style" key on the other side of the circuit board. If you remove the board to check the button operation...make sure that the little small chip doesn't fall out (you can see it circled in black in the 2nd image below). If it does...YOU WON'T BE ABLE TO START YOUR CAR. This has happened to at least 3-4 people over the past year on the various forums I read.

BTW...some early build models may use TW0 1220 batteries instead of the single 2016...so briefly removing the cover to check will prevent the purchase of the wrong battery.

(images below by: anncam/bimmerforums)

(if you remove the circuit board...don't lose the EWS transponder chip {circled in black} which sits loose inside the key down near the key blade)

See also:
- How to replace the old-style BMW E39 square keybattery (1) (2) (3) & how to replace the rubber key pads in the old style square keys (1) (2) & opening, charging, recoding, & battery replacement (1) of the new-style diamond key (1) (2) (3) (4) (5) (6) & how to recharge off your BMW and how long a BMW key will last in the drawer before it needs that off-the-car recharging (1) & converting the old-style square key to the newer diamond shaped key (1) & the details on swapping the BMW diamond key transponder (1) & proper diamond key initializing (1) (2) & what to do if your key is locked inside your bimmer (1) & a description of the various types of BMW Remote, Illuminated, Spare/Wallet, & Valet/Service keys (1) (2) & a list of diamond key EWS, FZV, & DWA functions (1) (2) & all about the 10-key limit to programming your own keys at home (1) & a description of the ignition key ISN (individual serial number) ten-second rule (1) & what to do if you lost your only diamond key (1) or what to do if your BMW key was stolen (1)

I took the liberty of modifying the pictures in this thread, and from others, to create this composite informative picture, so that others benefit from every action.
See also:
- How to replace the old-style BMW square keybattery (1) (2) & how to replace the rubber key pads in the square keys (1) (2) & what the red LED indicates on the old square key (1) & what can go wrong with a key and where to send it for repair (1) (2) (3) (4) & what battery to use in the new style 2000+ BMW E39, E46, E53, E85, etc. diamond key (1) (2) (3) (4) (5) (6) (7) & youtube videos of diamond key repairs (1) (2) (3) & a square key to diamond key retrofit and transponder swap (1) (2) (3) (4) & diamond key to square key retrofit questions (1) & how to recharge your key out of your BMW and how long that key will last in the drawer before it needs that off-the-car recharging (1) & the details on swapping the BMW diamond key transponder (1) & the proper diamond key initializing or programming sequence (1) (2) (3) (4) (5) (6) & what to do if your only key is locked inside your bimmer (1) & a description of the various types of BMW Remote, Illuminated, Spare/Wallet, & Valet/Service keys (1) (2) & a list of diamond key EWS, FZV, & DWA functions (1) (2) & all about the 10-key limit to programming your own keys at home (1) & a description of the ignition key ISN (individual serial number) ten-second rule (1) & what to do if you lost your only diamond key (1) or what to do if your BMW key was stolen (1)

Any power supply that has 3 Volts nominal will be fine for the key. However, in the three cases of key repair I have done, the problem was always the battery prongs losing contact with the board. The battery is heavy and eventually breaks free. I resoldered them and put a bit of padding on top. If you need to change the battery, reuse the prongs. Ask the battery shop to point solder them on the new battery for you.